This invention relates to drilling derrick assemblies and more particularly relates to those drilling derrick assemblies that are portable and have masts that are to be erected for use in oil field drilling operations.
The drilling derricks or masts must be portable because they are to be used in remote locations to meet the oil field operational requirements. Such portable drilling derricks are transported with extreme difficulty and often the transportation can only be accomplished by helicopter or through the use of small trucks that are able to wend their way to the outermost reaches of desolate areas where the sites of drilling operation are often found. Thus, the mast and all the other rig components must be as light in weight as possible to meet such difficult transportation requirements, yet be erectable with a minimum of equipment and skilled personnel.
The transportation of an erected vertical mast is well known to be unfeasible and therefore these drilling masts are broken down usually through a variety of conventional methods for shipping to the location, or as nearby as practical, and thereafter erecting the mast for use. The methods chosen for erecting the mast often depend upon the size and capacity of the mast, the method of transport to be used and the equipment available at the drilling location to assist with the assembly.
The combination of minimum weight and ease of erection poses an extremely difficult problem in the art when drilling derricks are expected to be sturdy and provide sufficient support for the drilling operation. Not only does the mast pose a problem of achieving the required strength with minimum weight but also all of the erection power equipment, whether draw works or power rams, must be powerful enough to supply the force to raise the elongated mast from its horizontal, but fully elongated or set up position to the final vertical position. The torque required to raise the set up mast to the vertical position is of such magnitude that the power equipment and the substructure must be able to withstand the high forces that would be attributable to such a raising. Such sturdy and powerful equipment must inherently therefore be so very heavy that portability suffers greatly.
Telescopic drilling masts have been conventionally used in an effort to meet transportation requirements. These masts are nested within one another such as is disclosed in the patent issued to Woolslayer 2,577,642. In this patent, the masts, though shown to be transported by truck in a nesting or telescopic position must, prior to being raised, be extended by mast sections so that they may be secured together while still in a horizontal position. Thereafter the rams or draw works used to raise the elongated horizontal mast are activated to raise the elongated mast to the vertical position. Such rams or draw works would then have to overcome the very substantial torque presented by the horizontal mast, and thus would require great force necessitating the undesirable heavier and more powerful substructure and raising apparatus.